A point source emits sound equally in all directions in a non-absorbing medium. Two point `P` and `Q` are at distance of `2 m` and `3 m` respectively from the source. The ratio of the intensities of the wave at `P` and `Q` is :

Options

A. `3:2`
B. `2:3`
C. `9:4`
D. `4:9`

Answer

C

Explanation

Intensity =Energy /sec/unit area
Area `prop r^2 implies I prop 1//r^2`
`implies I_1/I_2=r_2^2/r_1^2=3^2/2^2=9/4`